This invention relates to superabsorbing polymers based on L-aspartic acid in synthetic fiber and film forms and to process(es) for preparing such fibers and films.
Polysuccinimide (PSI) is prepared by thermal polycondensation of L-aspartic acid which can then be base-hydrolyzed to polyaspartate salt which has many industrial uses such as lubricant in metalworking fluids. Crosslinking PSI before or after hydrolysis renders the hydrolyzed salt superabsorbent in that it can absorb many times its weight of liquid such as water. This capability of absorbing significant quantities of fluids, including body exudates and aqueous compositions of all kinds, creates another important class of application for these polymers in products such as diapers, sanitary napkins, incontinence products, towels, tissues and the like. These superabsorbing polymers are in the prior art as typically disclosed in U.S. Pat. No. 5,461,085 (Nagatomo et al); U.S. Pat. No. 5,525,703 (Kalota) and U.S. Pat. No. 5,612,384 (Ross et al). Though articles of superabsorbing polymers derived from L-aspartic acid are recognized in this art as desirable, to date they are only disclosed in unshaped, particulate form as recovered from the hydrolysis step forming the salt. Note all the examples of the patents referenced above. Continued absence in the art of these polymers in fiber or film form is likely due to the important conflicting requirements of being sufficiently plastically extensible to permit drawing fiber or forming film while being crosslinked and hydrolyzed to create superabsorbency.
In view of the noted applications, it would be highly desirable to provide biodegradable superabsorbent polymers derived from L-aspartic acid in fiber or film form to facilitate formation into products such as diapers and the like.
The superabsorbent fibers and films of the present invention provide a solution to many problems encountered with unshaped, particulate superabsorbent polymers derived from L-aspartic acid. For example, the superabsorbent fibers of the invention have the advantages of (1) avoiding the problem of migration by having the ability to entangle with fluff pulp fibers, (2) being compatible with other fibers resulting in greater flexibility in applications and fabrication, and (3) having a large surface area resulting in a faster absorption rate. For example, the superabsorbent films of the invention have the advantage of avoiding the problem of migration by having the ability to remain stationary within an article containing the film.